1. Field
The present disclosure relates to light sources, and more particularly to a driver-free light-emitting devices.
2. Background
Solid state devices, such as light emitting diodes (LED)s, are attractive candidates for replacing conventional light sources such as incandescent, halogen and fluorescent lamps. LEDs have substantially higher light conversion efficiencies than incandescent and halogen lamps and longer lifetimes than all three of these types of conventional light sources. In addition, some types of LEDs now have higher conversion efficiencies than fluorescent light sources and still higher conversion efficiencies have been demonstrated in the laboratory. Finally, LEDs require lower voltages than fluorescent lamps and contain no mercury or other potentially dangerous materials, therefore, providing various safety and environmental benefits.
More recently, solid state devices have been used to replace high-intensity discharge (HID) lamps to provide high levels of light over large areas when energy efficiency and/or light intensity are required. These areas include roadways, parking lots, pathways, large public areas, and other outdoor applications. To increase the intensity of light in these applications, often more than one solid state light emitter is arranged in a package. An example of a solid state light emitter is a light emitting semiconductor chip comprising a p-n junction. An example of a package is a collection of light emitters arranged on a substrate and encapsulated in a phosphor to produce broad spectrum white light. This package is sometimes referred to as an “LED device.” A heat sink is often attached to the LED device to dissipate heat generated by the light emitters.
LED devices are subject to various safety testing requirements prescribed by different authorities such as Underwriter Laboratories (UL), Conformite Europene (CE), and the like. In some of these testing procedures, the LED device must withstand a high potential between the substrate and the heat sink. If the LED device design is unable to withstand the required voltage, an isolated driver may be required to power the LED device. An isolated driver, typically referred to as a “Class 2 driver,” provides electrical isolation between the primary power source (e.g., wall plug) and the LED array. If, on the other hand, the LED device design is capable of withstanding the required voltage because sufficient isolation may be achieved between the LED device and heat sink, a non-isolated driver may be used to power the LED device. A non-isolated driver, typically referred to as a “Class 1 driver,” is less expensive than a Class 2 driver, and therefore, reduces the manufacturing costs. However, an LED device design that eliminates the need for a driver altogether would provide further cost benefits, as well as improve reliability, reduce maintenance, and simplify the conversion from conventional light sources currently being used in incandescent, fluorescent, halogen, (HID), and other similar lamps to solid state light emitters.